The present invention relates to an electric braking apparatus for producing braking force by torque of a motor, and particularly to an electric braking apparatus added with a parking brake function.
There are currently electric braking apparatuses with a caliper comprising a piston, a motor and a rotation-linear movement conversion mechanism for converting rotation of the motor into linear movement. In such an electric braking apparatus, the piston is moved in accordance with rotation of a rotor of the motor to thereby press a brake pad against a disk rotor and produce braking force. Further, such an electric braking apparatus normally has a sensor for detecting pressing force or a stroke distance of a brake pedal depressed by an operator and controls the amount of the rotation (a rotational angle) of the electric motor in accordance with the detection results detected by the above sensor to thereby achieve the desired braking force.
However, in recent times, there have been various attempts made to enhance the functionality of an electric braking apparatus of this kind by adding the parking brake function. For example, U.S. Pat. No. 5,348,123 and corresponding German Patent Laid-open No. (Offenlegungsschrift) DE4229042A1 have proposed a mechanical brake operating mechanism in which a rotating shaft is connected to a pivoting member of the rotation-linear movement conversion mechanism described above via a clutch mechanism and a ball ramp mechanism. A rotational force is exerted on the rotational shaft from the outside by an operation of, for example, a lever, to engage the clutch via the ball ramp mechanism, thereby placing the rotation-linear movement conversion mechanism in operation to produce braking force.
However, in the mechanical brake operating mechanism described in the above publications, when the brake pedal is depressed while the parking brake is made effective by the operation from the outside, the problem arises that since the rotation-linear movement conversion mechanism is operationally connected to the outside operating portion via the clutch mechanism, the electric brake does not operate. Further, it is also a problem that since the rotating shaft is connected in series to the pivoting member of the rotation-linear movement conversion mechanism via the clutch mechanism and the ball ramp mechanism, the caliper is elongated in the axial direction. Therefore, the mechanical brake operating mechanism may not be suited for all vehicles due to possible interference with the wheel.
The invention has been made in view of the above-described technical background. It is a purpose thereof to provide an electric braking apparatus equipped with a parking brake function that does not interfere with the normal braking operation of the braking apparatus. It is still another purpose thereof to provide an electric braking apparatus that can be mounted on any vehicles.